CMV retinitis

Definition

Cytomegalovirus (CMV) is a member of a group of herpes-type viruses that can cause many diseases, including retinitis (an inflammation of the retina of the eye).

Causes

Cytomegalovirus, also known as CMV, is very common. The majority of adults have antibodies to CMV in their blood (indicating they have been infected) by age 40. Usually, CMV produces no symptoms. However, serious CMV infections can occur in people with impaired immunity (immunocompromised hosts), such as those with AIDS.

People undergoing chemotherapy, which weakens the immune system, or those receiving immunosuppressive drugs for bone marrow or organ transplants, are also vulnerable.

One serious CMV infection is CMV retinitis, which can cause blindness. Retinitis usually begins in one eye, but often progresses to the other eye. Without treatment, progressive retinal destruction will lead to blindness in 4 to 6 months.

Even with continuous treatment, the disease can become worse, causing blindness. This may be because the virus becomes resistant to the drugs, so that the drugs are no longer effective, or because the patient's immune system has deteriorated further.

Patients with CMV retinitis also have a 25-40% of developing retinal detachment, in which the retina detaches from the nerves of the eye, causing blindness. Systemic CMV infection can also occur.

About 25% of people with AIDS develop CMV retinitis. Therefore, AIDS patients with a CD4 count of less than 100 cell/ mm³ should be examined periodically for retinitis, even if they have none of the symptoms listed below.

An AIDS patient (especially one with a very low CD4 count) who has visual disturbances should seek medical attention and arrange for an exam.

Symptoms

Note: Many patients with CMV retinitis have no symptoms.

• floaters (small spots in the vision)
• decreased visual acuity
• loss of peripheral vision
• blurred vision
• blind spots

Exams and Tests

CMV retinitis is diagnosed through a standard ophthalmologic exam. Dilation of the pupils and indirect ophthalmoscopy will show signs of CMV retinitis.

Diagnosis of CMV infection can be made through the following tests:

• Blood or urine culture: a blood or urine sample is cultured to see if it will grow the virus in the laboratory. Results take as long as 3 weeks.
• CMV PCR: this is a blood test that detects the presence and amount of CMV in the blood.
• CMV antigenemia test: this blood test detects the viral particles on the surface of white blood cells. This can indicate if the virus is replicating in the body or is inactive.
• CMV serology: this test detects CMV antibodies in the blood. Most people have two types of antibodies, IgG (which indicate old infection) and IgM (which indicate new infection).
• Tissue biopsy for culture: a biopsy of the tissue (often from the lung or stomach) that CMV is thought to have infected is cultured in the laboratory to see if it will grow the virus. This tissue can also be examined in the laboratory for evidence of viral infection and presence of CMV viral particles.

Treatment

The objective of treatment is to prevent progression of the disease, which can lead to blindness. Therapy must be continued indefinitely, or until blindness occurs. Intravenous ganciclovir, foscarnet, and cidofovir have all been shown to improve CMV retinitis.

Once the patient is improving, the oral formulation of the drug, called valgancioclovir, may be taken instead, although CMV is sometimes resistant to these drugs. Also, ganciclovir can deplete white blood cells, and cidofovir and foscarnet can cause kidney damage.

Ganciclovir and foscarnet can also be given as intravitreal implants, which are small capsules of medications surgically inserted into the eye. They deliver a very high dose of medication to the eye.

Oral anti-CMV agents should be taken along with the implants, which must be changed every eight months. These implants have been shown to be beneficial in reducing progression of CMV retinitis.

Fomivirsen, a drug recently approved by the FDA, is injected directly into the eye.

Outlook (Prognosis)

Progression of the disease is common, even when therapy continues, because antiviral medications stop the replication of the virus but do not destroy it. CMV is itself immunosuppressive and may worsen the symptoms of other causes of immunosuppression

Possible Complications

• retinal detachment
• blindness
• low white blood cell count with use of ganciclovir
• kidney impairment with use of foscarnet

When to Contact a Medical Professional

If symptoms worsen or do not improve with treatment, or if new symptoms develop, call your health care provider.

Prevention

Symptomatic CMV infection normally occurs only in immunocompromised individuals. Avoiding the primary cause of immune deficiency, AIDS, will therefore prevent symptomatic CMV infection.

Individuals with HIV should begin anti-HIV medications. Individuals undergoing chemotherapy, taking anti-rejection medications for transplant, or undergoing cortisone therapy should report any visual abnormalities to their doctor.